The present invention relates to a head gimbal assembly (HGA) which includes a head slider and a suspension which supports the head slider, and more particularly to a technique which electrically connects the head slider and the suspension.
A magnetic disc device includes a magnetic disc which stores data and a head slider which gets access to the magnetic disc. In the head slider, a head element part which performs the reading and/or the writing of data between the head slider and the magnetic disc is formed. The head element part includes a recording element which converts an electric signal into a magnetic field in response to recording data to the magnetic disc to an electric signal. The magnetic disc device further includes a head arm which moves the head slider to a desired position on the magnetic disc. The head arm is driven by a voice coil motor (VCM). By rotating the head arm about a rotary shaft, the head slider is moved in the radial direction of the magnetic disc. Accordingly, the head element part can access a desired track formed on the magnetic disc and perform the reading/writing process of data.
The head arm includes a suspension which possesses resiliency, while the head slider is fixed to the suspension using an adhesive agent. By establishing a balance between the pressure attributed to the viscosity of air between an air bearing surface (ABS) of the head slider which faces the magnetic disc in an opposed manner and the rotating magnetic disc and the pressure which is applied in the magnetic disc direction due to the suspension, it is possible to allow the head slider to float over the magnetic disc with a fixed gap. The parts constituting the head slider and the suspension which supports the head slider are referred to as a head gimbal assembly (HGA).
FIG. 7 shows an example of an HGA as viewed from a recording surface side of the magnetic disc. As shown in FIG. 7, the HGA 400 includes a head slider 401, a suspension 402 and a lead 403. The lead 403 is conductive wiring for transmitting signals between a head element part (not shown in the drawing) formed on the head slider 401 and an amplifying part (not shown in the drawing). The suspension 402 includes a flexible flexure 404 which holds the head slider 401 on a magnetic-disc-facing-surface side, and a load beam 405 which holds the flexure 404 on the magnetic-disc-facing-surface side. The HGA 400 shown in the drawing is of a loading/unloading type, wherein a tab 406 which contacts a ramp mechanism is provided to a distal end of the load beam 405. A plurality of bonding pads are connected to the head element part and formed on a front surface (tab side) of the head slider 401. The respective bonding pads of the head slider 401 and the bonding pads formed on a distal end of the lead 403 are connected with each other by ultrasonic bonding which uses gold balls, solder ball bonding (SBB) which bonds the bonding pads by reflowing solder balls or the like. Among these bonding techniques, the technique to join the head slider and the lead by the ultrasonic bonding using gold balls or the like is disclosed in JP-A-2000-251217 (Patent document 1) for example.
In the conventional magnetic disc device, the lead which connects the head element part and the amplifying part requires 2 lines for transmitting recording signals and 2 lines for transmitting reproducing signals, that is, 4 lines in total. In this case, the number of bonding pads formed on the head slider is 4. However, a head slider having a TFC (Thermal Flying height Control) technique requires additional lines and hence, it is necessary to form at least 6 bonding pads on the head slider.
FIG. 8(a) is a view showing a side end surface of a conventional head slider 401 on which 6 bonding pads are formed. Further, FIG. 8(b) is a cross-sectional view taken along a line P-Q in FIG. 8(a). As shown in FIG. 8(a), on the side end surface 401c of the head slider 401, 6 bonding pads 408 which connect the head element part 407 and the leads 403 are formed. To be more specific, as shown in FIG. 8(b), the bonding pad 408 is formed on a surface of a protective film 411 made of alumina (Al2O3). The protective film 411 is formed on a side surface of a head slider body 410 made of ALTIC (AlTiC) and plays a role of protecting the head element part 407. Here, ALTIC is a sintered body of aluminum (Al), titanium (Ti) and carbon (C) and is a type of ceramic which is obtained by baking alumina, titanium carbide.
Further, the bonding pads 408 are formed at a position which is spaced apart from a back surface 401b of the head slider 401 by a predetermined distance A (A>0). Here, the back surface 401b is a surface on a side opposite to an ABS 401a which is a surface floating above the magnetic disc. On the other hand, bonding pads 409 are formed on an end portion of the leads 403 and are electrically connected with the bonding pads 408 formed on the head slider 401. Here, as shown in FIG. 8(b), a bonding surface of the bonding pads 409 is formed to be substantially orthogonal to the side surface 401c of the head slider 401 and the bonding surface of the bonding pads 408. Further, the bonding pads 408 and the bonding pads 409 are spaced apart from each other by a predetermined distance D (D>0). Hereinafter, the distance D is referred to as pad clearance. In the conventional HGA, the pad clearance is set to approximately several ten μms.
In the connection using solder such as solder ball bonding or the like, it is necessary to avoid the occurrence of defective connection. The defective connection implies a state in which pads are not yet electrically connected or the connection between pads is insufficient. The increase of defective connection in the solder ball bonding leads to the lowering of a yield rate of the HGA manufacturing steps.
As described above, the number of lines to be connected to the head slider is increasing. When the number of lines connected to the head slider is increased, it is necessary to increase the number of bonding pads formed on the surface of the head slider and hence, the restriction imposed on the size of respective bonding pads becomes stricter. For example, with respect to a size of a side surface of a femto head slider, a width of the slider is 0.7 mm or less and a height of the slider is 0.23 mm or less and hence, to form 6 bonding pads on the head slider, it is necessary to restrict a width of the pads to approximately 80 μm. In bonding these bonding pads using solder balls, a diameter of the solder balls becomes approximately 90 μm.
When the size of the bonding pads which contribute to the connection by soldering becomes small due to the increase of the number of pads formed on the head slider, the miniaturization of the head slider or the like, there arises a drawback that a yield rate is deteriorated due to the increase of defective connections. It is known that the occurrence ratio of defective connections at the time of bonding using soldering depends on the distance between the bonding pads formed on the head slider and the bonding pads formed on the suspension-side leads.
Here, in the connection using gold balls, there exists no dependency relationship between the defective connections such as the connections using solders and the distance between the bonding pads. In case of gold ball bonding, the bonding of the bonding pads and the gold balls is performed in a state that a spherical shape of the gold ball is substantially maintained and hence, even when the pad clearance is set to a value close to a radius of the gold ball, the occurrence ratio of the defective connection is not changed.